Subj : DAY1SVR: Day 1 Convective Outlook To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sat Oct 14 2023 12:48:16 ACUS01 KWNS 141248 SWODY1 SPC AC 141246 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0746 AM CDT Sat Oct 14 2023 Valid 141300Z - 151200Z ....THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS OVER PORTIONS OF EASTERN NORTH CAROLINA... ....SUMMARY... Potential exists for damaging to marginally severe gusts and/or a tornado today over portions of eastern North Carolina. ....Synopsis... Over the CONUS, amplification of the mean mid/upper-level pattern is expected through the period, as a ridge builds over the West, and a series of shortwave troughs contributes to net height falls and cyclonic flow over a broad area from the Gulf Coast to the Great Lakes and Atlantic Seaboard. The two strongest of those shortwave troughs are apparent in moisture-channel imagery over: 1. Portions of WI/IL/MO, with a weak 500-mb low over northern IL. This feature will continue to devolve to an open-wave trough and lose amplitude, crossing the upper Ohio Valley and central Appalachians early this evening, then the Mid-Atlantic Coast around 06-9Z. 2. Western SD initially, with an at least intermittently closed 500-mb low moving southeastward to east-central NE by 00Z, then southwestern MO around 12Z tomorrow. Approach of the leading mid/upper perturbation will strengthen an initially weak, frontal-wave surface low, analyzed at 11Z over eastern SC between SSC-CHS at 11Z. A cold front was analyzed from that low south-southeastward across Atlantic waters then bending southwestward over south-central FL to the central Gulf. An occluded front extended from the SC low into a broad area of low pressure over OH/IN/IL, under and ahead of the midlevel circulation center. A warm front was drawn from the SC low northeastward along or just south of the southern coast of NC and past HSE. A shallow stable layer in the 12Z MHX RAOB, with light southeast winds, indicated the boundary was just south of there, near the immediate beaches. The warm front should spread inland through the afternoon, but probably in a diffuse and erratic manner because of precip to its north. By 00Z the coastal low and warm front should move northeastward to near Cape Charles/southernmost Delmarva region, with cold front southward over easternmost NC. This low and the warm front should shift offshore thereafter. ....Eastern NC... Ongoing precip is apparent in irregularly sized patches over the eastern Carolinas, especially NC. Little or no thunder has occurred in the last few hours, likely related to a layer of poor midlevel lapse rates well-sampled by the 12Z CHS sounding. This activity, and associated areas of clouds/precip, will substantially limit diabatic heating for much of the day across the outlook area. However, the low-level airmass in the cloud/precip area, while characterized by stable to neutral lapse rates initially, only needs weak heating and warm/moist advection to yield enough theta-e for surface-based effective-inflow parcels to overcome the weak midlevel lapse rates. That should occur, with upper 60s to low 70s F surface dewpoints spreading northward/inland over eastern NC east through southeast of the low. 500-1000 J/kg MLCAPE is possible in a narrow plume ahead of the cold front, which also may support a conditional second round of convection along the front, in a broken arc. Effective-shear magnitudes of 45-55 kt suggest some of the convection may become supercellular -- especially whatever can remain discrete through maturity. In both cases (leading plume and possible frontal follow-up), forecast soundings suggest hodographs will be well-curved but not particularly large, leading to marginal SRH with values such as: effective and 0-3 km of 100-300 J/kg, and 0-1-km of 75-150 J/kg. Vorticity enhancement along favorably positioned outflow/ differential-heating boundaries may contribute to some local maxima in storm-scale rotation and tornado potential, but this threat appears quite conditional and isolated. The most intense cells also may produce damaging winds, and a severe gust cannot be ruled out. ...Edwards/Broyles.. 10/14/2023 $$ = = = To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. Otherwise email Chris Novy at cnovy@cox.net and ask to be removed from WX-STORM. --- SBBSecho 3.14-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .